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TDA7388 - DC on output at power on
TDA7388 - DC on output at power on
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Old 21st October 2020, 10:33 AM   #1
selwe is offline selwe
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Default TDA7388 - DC on output at power on

I populated a board bought from ali.. which seems to me to be using datasheet scheme. For C9, C10 I used bipolar as in datasheet (the silkscreed shows them polar). For the input caps i used some 10uF muse I had around and for C7 I used a stack of 3x1000uF. The problem is I get plenty of DC on outputs when I power it on. It lasts for a few seconds (3-4) then it disappears and the music starts playing. Any ideeas what it could be? The IC is original from digi.
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Old 21st October 2020, 11:35 AM   #2
Mooly is offline Mooly  United Kingdom
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TDA7388 - DC on output at power on
The chip has bridged output stages and so it is normal to see around half the supply voltage on each output pin.

Because the speaker is connected between these outputs it always sees zero volts across it.

So it all sounds normal to me
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Old 21st October 2020, 12:30 PM   #3
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Thanks for input.
Here are some maximum readings on two outputs, 1-2 seconds after power on. This is what I get if there is an input signal. If there is no input signal then the readings go to about 1V DC. After this peak, it slowly decreases in about 40 seconds to acceptable values (<40 mV). The speakers were not connected during the readings.
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Last edited by selwe; 21st October 2020 at 12:33 PM.
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Old 22nd October 2020, 08:30 PM   #4
ubergeeknz is offline ubergeeknz  New Zealand
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Tried using the specified values on the inputs?
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Old 23rd October 2020, 07:29 AM   #5
Mooly is offline Mooly  United Kingdom
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TDA7388 - DC on output at power on
The behaviour of it all sounds pretty normal.

The data sheet mentions it has anti pop circuitry and I think the time constant is determined by the SVR cap on pin 11............... which is a bit confusing as two data sheets have different pin outs.
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Old 23rd October 2020, 10:39 AM   #6
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Quote:
Originally Posted by ubergeeknz View Post
Tried using the specified values on the inputs?
I admit I used very big caps (for this application) on inputs (10uF) only because I had them around. ...But, rising the capacitance of input caps just lowers the high pass frequenc; any dc won't pass through these caps, no matter their values (anyway, I used a smartphone headphone output as a signal source, so I think the signal is quite clean).
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Old 23rd October 2020, 10:45 AM   #7
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Quote:
Originally Posted by Mooly View Post
The behaviour of it all sounds pretty normal.

The data sheet mentions it has anti pop circuitry and I think the time constant is determined by the SVR cap on pin 11............... which is a bit confusing as two data sheets have different pin outs.
Uh, oh, that's interesting. I think the latest datashet should be more accurate - the revision date should be written somewhere (at the begining, I think) in datasheet.
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Old 23rd October 2020, 12:05 PM   #8
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Latest datasheet version I could find.
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